Fuel injection systems for internal combustion engines



l l I l J. MAIR FUEL INJECTION SYSTEMS FOR INTERNAL COMBUSTION ENGINESFile dJan. 31. 1968 May 26, 1970 Inventor I65 6PM M A g y ,1.\ Wu. w W

INJ'ECTORS.

DISTRIBUTOR PULSE AMPLIFIER United States Patent O 3,513,815 FUELINJECTION SYSTEMS FOR INTERNAL COMBUSTION ENGINES Joseph Mair,Leamington Spa, England, asslgnor to Associated Engineering Limited,Leamington Spa, England, a British company Filed Jan. 31, 1968, Ser. No.702,032 Claims priority, application Great Britain, Feb. 7, 1967,5,878/67 Int. Cl. F02b 3/00 US. Cl. 123-32 11 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a fuel injection system forinternal combustion engines comprising at least one electromagneticallyoperated fuel injector and a control pulse generator producing pulsesfor energising said at'least one injector, so that the injector or ainjector is opened for a period depending on the duration of each of thepulses to pass fuel to the engine, wherein means are provided forcompensating for the effect of supply voltage variations on the timethat an injector is open in response to a pulse from the control pulsegenerator, whereby the fuel delivery from the or each injector issubstantially independent of variations in said supply voltage.

The present invention relates to fuel injection systems for internalcombustion engines and more particularly to improvements in the fuelinjection systems such as are described in US. Pats. Nos. 3,240,191 and3,272,187.

Such systems comprise at least one electromagnetically operated fuelinjection valve or injector and a control circuit producing pulses forenergising said at least one injection valve so that the valve or avalve is open for a period depending on the duration of each of thepulses to pass fuel to the engine. The control circuit is fed with atleast one variable voltage which varies as a function of one or moreparameters of engine operation and which controls the duration of thepulses produced by the control circuit which are fed to energise theinjection valve or valves. As specifically described, the controlcircuit comprises a monostable multivibrator for producing theelectrical pulses and the duration of the pulses is varied by varyingtwo control voltages applied to the timing capacitor circuit of themultivibrator. The two control voltages may be derived from a computercircuit fed with a plurality of signals which respectively vary withvariations in different parameters of engine operation.

The fuel injection valves are solenoid operated devices and variationsin the voltage of the vehicle battery have been shown to cause avariation in the opening time of the valves, and hence produce avariation in fuel delivery through a valve for any chosen pulse durationor width. Therefore the quantity of fuel fed to the engine is no longersolely determined by variations in engine operating parameters, as isdesired.

Thus it has been found that for a fixed injector design, the solenoidcurrent builds up to a greater level during the first millisecond as thebattery supply voltage increases, with the result that the injectoropens more rapidly at increased supply voltages and delivers more fuelfor a given pulse duration or width. This reduction in opening time forany given increase in supply voltage is however the same for all pulsedurations or widths.

According to the present invention, means are provided for compensatingfor the eifect of supply voltage variations on the time that an injectoris open in response to a pulse from the control pulse generator, wherebythe fuel delivery from the or each injector is substantially independentof variations in said supply voltage.

3,513,815 Patented May 26, 1970 Where the control pulse generatorcomprises a monostable multivibrator, means are provided for varying abias applied to the monostable multivibrator with changes in batterysupply voltage, in order to keep the fuel delivery more nearly constant,as determined by the control parameters, with variations in the batterysupply voltage.

Preferably the bias applied to the monostable multivibrator is derivedfrom a network connected across the voltage supply and according to afeature of the present invention, this network includes a non-linearelement such as a saturated diode or a Zener diode.

The invention will now be further described by way of example withreference to the accompanying drawing which is a simplified diagram ofone embodiment of fuel injection system according to the presentinvention.

The system basically comprises a control pulse generator 1, a computer2, a pulse amplifier 3, a distributor 4 and fuel injectors 5, andoperates generally in the manner described in Pat. No. 3,272,187.

As described in that application, the system is intended for a fourcylinder internal combustion engine and a separate fuel injector isprovided for each cylinder. The injectors are preferably mounted in theinlet manifold of the engine.

The duration of the pulses fed to energise the injectors, via theamplifier 3 and distributor 4, is controlled by the control pulsegenerator 1, which is in turn controlled by two voltages V1 and V2derived from the computer 2. The control pulse generator is triggered bypulses at the firing frequency of the engine and the computer 2 is fedwith information supplied by a number of transducers, each responsive toone or more conditions of engine operation. Since the injectors aresupplied with fuel at constant pressure, a periodic activation of aninjector for a time dependent upon engine operating conditions, asdetermined by voltages V1 and V2, will meter the fuel supplied to theengine through each injector.

The control pulse generator 1 is basically similar to that shown in FIG.2 of the aforementioned copending application, and is in the form of amonostable multivibrator circuit comprising transistors TRl and TR2 andincluding the timing capacitor C1, which during the timing period isdischarged through the constant current transistor TR4. In the steadystate or rest condition of the circuit, transistor TR2 is held in thenormally ON condition, its base current being supplied by the collectorcurrent of the NPN transistor TR4. At this time, transistor TRl is heldOFF by a negative bias voltage Vb supplied from the voltage dividernetwork P connected across the battery supply voltage Vs. In practice,this network may be located in the computer circuit. When anegative-going trigger pulse is applied to the base of transistor TRl,it is turned ON and transistor TR2 is turned OFF. This state of themultivibrator circuit will be maintained until capacitor C1 hasdischarged through transistor TR4 to a voltage which is sufiicient toturn transistor TR2 ON again, whereupon the circuit reverts to itsoriginal state and the pulse is terminated. Transistor TR3 provides alow impedance charge path for capacitor C1 when transistor TR2 is turnedON.

The duration of the pulses produced by the multivibrator is determinedby the voltage change across capacitor C1 and the discharge currentthrough transistor TR4. The control of the voltage change acrosscapacitor C1 is effected by a control voltage V1 derived from thecomputer circuit and dependent, for example, upon inlet manifoldpressure, engine speed and acceleration. The discharge current throughtransistor TR4 is varied by control voltage V2 also derived from thecomputer circuit and varying, for example, in dependence with enginewater temperature, air temperature, a starting enrichment signal and anidling enrichment signal.

The operation of the circuit so far described is generally similar tothat described in the aforementioned application. However, in thatapplication the bias voltage Vb applied to the emitter of transistor TRIis derived from a purely resistive voltage divider connected across thebattery supply voltage, and hence the fuel delivery through an injectoris substantially dependent on variations in the voltage of the batterysupply.

In accordance with the present invention, the voltage divider Pconnected across the battery supply voltage Vs includes a non-linearelement, such as Zener diode Z1. Since the voltage across the Zenerdiode remains practically constant as its current increases, the voltageacross the remaining resistive parts of the voltage divider increases inproportion faster than the supply voltage, including the bias voltage Vbwhich is developed across resistor Rb. In this way the bias voltageapplied to the emitters of transistors TRl and TR2 is increased at agreater rate than the supply voltage. The voltage change acrosscapacitor C1 which in part determines the pulse width is thus increasedat a lesser rate than the supply voltage, so that the width of the pulseenergising the fuel injection valves is reduced to compensate for theshorter opening time of the valves at the increased supply voltage. Thebias voltage decreases proportionally in a similar manner with decreasesin battery supply voltage. Since Zener diodes can be obtained with awide range of working voltages, a close approximation to the rightamount of compensation can be obtained to suit the characteristic of anyparticular type of fuel injector. In certain cases, for example where itis desired to set up the circuit particularly to provide a lower thannormal degree of compensation one or more forward conducting Zenerdiodes or saturated normal diodes may be used connected in series in thevoltage divider network.

By means of the present invention the fuel delivery from the or eachfuel injector is substantially independent of variations in the vehiclebattery voltage and varies only in accordance with the control voltagesapplied to the control pulse generator, as determined by parameters ofengine operation.

In the embodiment described it will be understood that at a fixed supplyvoltage Vs the relationship between the change in charge on thecapacitor and the output pulse Width is linear. The change in charge onthe capacitor is itself determined by the difference between controlvoltage V1 and bias voltage Vb.

I claim:

1. A fuel injection system for internal combustion engines comprising atleast one electromagnetically operated fuel injector and a control pulsegenerator producing pulses for energising said at least one injector, sothat the injector or a injector is opened for a period depending on theduration of each of the pulses to pass fuel to the engine, wherein meansare provided for compensating for the effect of supply voltagevariations on the time that an injector is open in response to a pulsefrom the control pulse generator, said compensating means comprisingmeans for varying a bias voltage applied to the control pulse generatorby a greater percentage in like polarity than a percentage variation ofthe total supply voltage, whereby the quantity of fuel injected by theor each injector is substantially independent or variations in saidsupply voltage.

2. A system is claimed in claim 1, wherein the control pulse generatorcomprises a monostable multivibrator and means are provided for varyinga bias applied to the monostable multivibrator with changes in thesupply voltage.

3. A system as claimed in claim 2, wherein the bias applied to themonostable multivibrator is derived from a network connected across thevoltage supply.

4. A system as claimed in claim 3, wherein said network includes anon-linear element such as a saturated diode or a Zener diode.

5. A system as claimed in claim 3, including a computer circuit fed witha plurality of signals which respectively vary with variations indifferent parameters of engine operation and which provides at least onevariable voltage fed to control the duration of the pulses produced bythe control pulse generator.

6. A system as claimed in claim 5, wherein said network connected acrossthe supply voltage forms a part of the computer circuit.

7. A system as claimed in claim 2, wherein the monostable multivibratorincludes a timing capacitor and is so arranged that the voltage changeacross the timing capacitor, which in part determines the pulse widthproduced by the multivibrator, is increased at a lesser rate than anincrease in the supply voltage, so that the width of the pulsesenergising the fuel injector or injectors is reduced to compensate forthe shorter opening time of an injector which occurs at an increasedsupply voltage.

8. In a fuel injection system for internal combustion engines comprisingat least one electromagnetically operated fuel injector and a controlpulse generator producing pulses for energising said at least oneinjector, so that the injector or a injector is opened for a perioddepending on the duration of each of the pulses to pass fuel to theengine, the improvement which comprises providing means for compensatingfor the effect of supply voltage variations on the time that an injectoris open in response to a pulse from the control pulse generator, saidcompensating means comprising means for varying a bias voltage appliedto the control pulse generator by a greater percentage in like polaritythan a percentage variation of the total suply voltage, whereby thequantity of fuel delivered by the or each injector is substantiallyindependent of variations in said supply voltage.

9. In a system as claimed in claim 8, the control pulse generatorcomprises a monostable multivibrator, means are provided for varying abias applied to the monostable multivibrator with changes in the supplyvoltage and the bias applied to the monostable multivibrator is derivedfrom a network connected across the voltage supply and including anon-linear element.

10. In a system as claimed in claim 9, a computer circuit fed with aplurality of signals which respectively vary with variations indifferent parameters of engine operation and which provides at least onevariable voltage fed to control the duration of the pulses produced bythe control pulse generator.

11. In a system as claimed in claim 9, the monostable multivibratorincludes a timing capacitor and is so arranged that the voltage changeacross the timing capacitor, which in part determines the pulse widthproduced by the multivibrator, is increased at a lesser rate than anincrease in the supply voltage, so that the Width of the pulsesenergising the fuel injector or injectors is reduced to compensate forthe shorter opening time of an injector which occurs at an increasedsupply voltage.

References Cited UNITED STATES PATENTS 2,910,064 10/1959 Schutte.

LAWRENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R. 123-119, 139

